1. Field of the Invention
The invention relates to avalanche diodes of the Read-type having a diode junction, an avalanche region, and a drift region.
2. Description of the Prior Art
What are now termed Read-type diodes were first disclosed by W. T. Read, Jr. in 1958 ("A Proposed High-Frequency Negative-Resistance Diode," W. T. Read, Jr., Bell System Technical Journal, March 1958, pp. 401-446). Since the original disclosure, numerous improvements in the attainable output power and dc to output signal power conversion efficiency have been made to the point where Read-type diodes have become useful in many microwave communications applications. Unfortunately, the applications in which Read-type diodes have heretobefore been employed have been greatly limited by the noisy output signals produced by previously available devices. For although prior Read-type diodes have been capable of producing higher output powers at greater power conversion efficiencies than other types of avalanche microwave oscillator and amplifier diodes, their noise measure has been so high as to prohibit their use in many systems where noise is an important consideration. Noise meausres of 60 db or greater were commonly found with previous devices whereas noise measures of 50 db or less are required in many important communications applications.
The causes of noise in the output signals from Read-type diodes have heretofore been imperfectly understood. In considering IMPATT-type avalanche diodes, it was known that the noise measure of such devices increased with increased operating temperature and power levels. It was also known that in Read-type diodes, the noise measure could vary considerably among diodes with different doping profiles. However, no theoretical treatment has appeared leading to the production of Read-type diodes having a predictable and controllable noise measure.